Massachusetts Unrestricted Construction Supervisor License Practice Test

In a single family dwelling, how many inches should a 6 mil vapor barrier be lapped between the base course and concrete floor slab?

1. 4 inches

2. 5 inches

3. 6 inches

4. 7 inches

The correct answer is: 6 inches

In residential construction, the installation of a vapor barrier is critical for preventing moisture from penetrating the living spaces of a building, particularly in areas where ground moisture can migrate through the foundation. The requirement for lapping a 6 mil vapor barrier between the base course and the concrete floor slab is established in building codes to ensure an effective seal against moisture intrusion. A 6-inch lap is the standard practice for this application. This dimension helps to ensure that there is adequate overlap, creating a continuous barrier that minimizes the risk of moisture entry. The wider lap can account for any shifting or settling of the materials, as well as provide extra coverage, enhancing the effectiveness of the vapor barrier. Inadequate lapping could lead to gaps that allow moisture to pass through, undermining the barrier's purpose. Therefore, adhering to the 6-inch standard is essential for maintaining the integrity of the moisture control measures in the construction of single-family dwellings. This requirement reflects best practices in residential construction and contributes to the long-term durability and comfort of the home.